Scale-Up Device For Testing Bit Balling Characteristics

ABSTRACT

An apparatus and method for testing the effects of mud chemistry and bit design on bit balling is disclosed The apparatus includes a replica bit coupled to a rotary drive and having at least one nozzle, a test container, a test formation located within the test container through which the replica bit will be drive, wherein the test formation includes a plurality of layers of pre-manufactured cuttings The apparatus further includes a lifting device applying a force to the bottom of the container to drive the test formation into the replica bit while the replica bit is rotating, a second container within which is a drilling fluid, and a pump for communicating drilling fluid from the container through a conduit to the replica bit.

When drilling in earth formations, solid materials such as “cuttings” (i.e., pieces of a formation dislodged by the cutting action of teeth on a drill bit) are produced

BACKGROUND OF INVENTION

When drilling in earth formations, solid materials such as “cuttings” (i.e., pieces of a formation dislodged by the cutting action of teeth on a drill bit) are produced.

Bit balling, also known as balling or balling up, refers to the collection of sticky consolidated material, usually drill cuttings, on drill pipe, drill collars, bits, etc. A bit with such material attached to it is often referred to as a “balled-up bit.” Balling up is frequently the result of inadequate hydraulic energy or undesirable interaction between drilling fluid and the cuttings.

Bit balling is one problem that is frequently encountered when drilling through clay. The problem is caused by the tendency of hydrated clay minerals to stick or adhere to the bit and bottom-hole assembly of a drill string. From an operations standpoint, bit balling is evidenced by increased pump pressures as the flow pathway through the well bore annulus becomes blocked, reduced rates of penetration, blocked shaker screens, a required over-pull tension that occurs due to a restricted annulus when tripping pipe, and possible stuck pipe.

Drilling rates can be significantly reduced by bit balling—the unwanted accumulation of reactive drill solids on the drilling surfaces and in the junk slots of the bit. Balling is mitigated by improving drilling fluid characteristics/properties and bit design. Optimization of the combined system in the laboratory can be expensive and time- consuming.

SUMMARY

In one aspect, the claimed subject matter is generally directed to a test apparatus for testing and studying the effects of mud chemistry and bit design on bit balling. The apparatus includes a replica bit coupled to a rotary drive and having at least on nozzle, a test container, a test formation located within the container through which the replica bit will be driven, wherein the test formation includes a plurality of layers of pre-manufactured cuttings. The apparatus further includes a lifting device for applying a force to the bottom of the test container to drive the test formation into the replica bit while the replica bit is rotated by the rotary drive, a second container within which is a drilling fluid, a conduit providing fluid communication from the second container to the replica bit, and a pump for circulating drilling fluid from the second container through the conduit to the replica bit.

In another aspect, the claimed subject matter is generally directed to a method of testing the effects of mud chemistry and bit design on bit balling. The method includes mixing a plurality of mixtures of ground rock material and reactive clay, layering the mixtures into a test container to create a test formation, coupling a replica bit to a rotary drive, fluidly connecting the replica bit to a second container containing drilling fluid, positioning the replica bit within the test container to a position above the test formation, rotating the replica bit, pumping fluid from the container to the replica bit, and lifting the test formation to the rotating replica bit so that the bit rotates into the formation.

Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the test apparatus.

FIG. 2 is a view of the test apparatus.

FIG. 3 is a side view of a replica bit.

FIG. 4 is a bottom view of a replica bit.

FIGS. 5 a and 5 b are a bottom and a side view of a replica bit with pointers showing the direction of replica bit nozzles.

FIG. 6 is a schematic of a bit balling cuttings sample maker.

FIG. 7 is a view of data that may be collected and/or calculated by a computer.

FIGS. 8-13 are photographs of replica bits with various degrees of balling.

DETAILED DESCRIPTION

The claimed subject matter relates to a test apparatus 10 for testing the effects of mud chemistry and bit design, hydraulics, weight on bit, and rotary speed on bit balling. Referring to FIGS. 1 and 2, the test apparatus 10 includes a rotary drive 12 coupled to a replica bit 14. The replica bit 14 is rotated by the rotary drive 12 through a test formation 16 located within a test container 18. A lifting device 20, such as an air cylinder, hydraulic cylinder, or other lifting mechanism may be located beneath the test container 18 and applies an upward force to the bottom of the test container 18. Thus, the test formation 16 is lifted towards and into the rotating replica bit 14 during testing. Drilling fluid (not directly shown) is contained in a second container 22. A pump 24 is used to circulate drilling fluid from second container 22 to replica bit 14. A camera 26 may be included to record video and/or still photographs for documentation of the test. A computer may be used to record data from the test and to perform calculations from the data as will be described.

Referring to FIGS. 3 and 4, a replica bit 14 is shown. The replica bit 14 may be of any reduced size. Applicants have found that a 2.5 inch replica was sufficient to simulate a full size polycrystalline diamond compact (PDC) bit. While a 2.5 inch replica bit was used, the invention is not limited by the size of the bit.

The replica bit 14 is a three-dimensionally printed, plastic model of a PDC bit. Referring to FIG. 5, the replica bit 14 includes at least one nozzle 28. In FIG. 5, the replica bit 14 includes nozzles 28 that are aimed in various directions, consistent with a full size actual PDC bit, as shown by the pointers 30 extending from each nozzle. The replica bit 14 is coated with stainless steel flakes or other metallic finish to simulate the metal from which actual PDC bits are comprised. Further, it is noted that tolerances on the printed replica bit are within acceptable tolerances of an actual bit.

When assembled into the test apparatus 10, the replica bit 14 drilling fluid is pumped through the replica bit 14 in a manner consistent with a full-sized PDC bit in a drilling environment. The nozzles 28 are in fluid communication with a conduit directing fluid into the bit. Drilling fluid is communicated towards the test formation 16 through the nozzles 28.

The test formation 16 includes pre-manufactured cuttings 32 made from ground rock material blended with predetermined concentrations of reactive clay and compressed for proper consistency. The distribution of particle sizes and formation characteristics are selected to simulate that achieved under actual drilling conditions. Referring again to FIG. 1, it can be seen that the test formation 16 may include a plurality of layers 34 of pre-manufactured cuttings 32. Each layer 34 may have a different ratio of ground rock material to reactive clay so that the layers higher in the formation have a greater amount of reactive clay than the layers lower in the formation. The layers that are lower in the formation may include a greater amount of ground rock material than the layers higher in the formation. Alternatively, the layers may be homogenous in as much as the layers may have the same amounts of ground rock material and reactive clay. The ground rock material may include shale and/or marble, for example. Further, the amount of reactive clay in the lower layers may be less than that of the higher layers.

Continuing to refer to FIG. 1, the test formation is created one layer at a time and each layer may be several inches thick. The lowermost layer may be made from a ground rock material, such as shale and/or marble, and an amount of reactive clay. The material is mixed and loaded into the test container 18. A piston or other weighted compression device is used to compress the mixture to a predetermined height or with a predetermined compressive pressure. A second layer of material may be mixed with the same amount or a lesser or greater amount of ground rock material or another material and a second amount of reactive clay, wherein the second amount of reactive clay may be less than, equal to, or greater than the first amount of reactive clay found in the lower layer. This second mixture is loaded into the test container 18 and a piston or other weighted compression means is used to compress the mixture to a predetermined height or with a predetermined compressive force. Successive layers are formed in the same manner.

Referring to FIG. 6, another way to create a test formation is shown. In FIG. 6, the test container 18 is located within an outer vessel 36. A stabilizing fluid 38 may be introduced between the test container 18 and the outer vessel 36 to remove any air between the two items. Seals 40 may be used to seal the interfaces between the test container 18 and the outer vessel 36. The fluid 38 may be pressurized to help prevent any deformation of the test container 18 when the pre-manufactured cuttings 32 are compressed. The material for the lowermost layer 34 of pre-manufactured cuttings 32 is mixed, as previously described, and poured into the test container 18. A piston 42 is used to compress the mixture to a predetermined height or with a predetermined pressure. A drain 44 may be included to bleed off any fluid.

The test container 18 is preferably cylindrical to represent the wellbore walls, although it may have other cross sectional shapes. The test container 18 may be transparent so that the test can be viewed and/or recorded by an external camera. When an external camera is to be used, the inner diameter of the test container 18 must be larger than the outer diameter of the replica bit 14 but not so much larger that the bit performance cannot be easily viewed through the container. It is noted, however, that if an external camera is not being used, the test container 18 need not be transparent.

The test container 18 may be retained such that it is able to rotate slightly with increasing torque. That is, as the replica bit 14 is rotated into the simulated formation, some amount of resistance may be transferred to the test container 18. The test container 18 may be provided with a torsion spring or similar mechanism to allow the test container 18 to rotate a relatively small amount, such as less than 25°.

The test container 18 containing the test formation 16 is lifted towards the replica bit 14 as the test is conducted. This may be performed by a lifting device 20, such as an air or hydraulic cylinder, located beneath the test container 18 or by another mechanism, such as a pulley system or rack and pinion, for example. Any device to lift the container relative to the longitudinally stationary replica bit 14 may suffice. This configuration advantageously allows a camera to be placed in a stationary location outside of the test container 18 and to capture bit performance. Alternatively, the test container 18 may be held longitudinally stationary while the replica bit 14 is driven rotationally into the simulated formation.

When the test formation 16 is created and testing is to begin, the replica bit 14 is coupled directly or indirectly to the rotary drive 12 and located within the test container 18 above the test formation 16. As previously discussed, a camera 26 may be used to document the test. Testing can be videotaped for documentation and detailed review. Referring to FIG. 2, the camera 26 may be mounted in a fixed location and, when used, would be focused on the replica bit 14. To aid in viewing the video or photograph, a solid color background 48 may be attached to the test fixture 50.

As testing is conducted sensors may be used to measure data that may be collected by a computer 46 and displayed on a monitor. Alternatively, data may be collected by another data collection device. Referring to FIG. 7, data collected may include time, torque on the replica bit 14, and revolutions per minute, i.e. rotary speed, of the replica bit 14. Further, the computer 46 may be used to perform various calculations used in the analysis of drill bits. For example, a Weight on Bit (WOB) calculation may be performed from data collected on the force being applied to the replica bit 14 by the test formation 16 as it is lifted towards the replica bit 14 and as the replica bit 14 “drills” through the test formation 16. A Rate of Penetration (ROP) may be calculated as the test is conducted based on the displacement of the test container 18. Mechanical Specific Energy (MSE) is the mechanical work required to excavate a unit volume of rock. MSE may be calculated based upon ROP, RPM, the diameter of the replica bit 14, and the torque. In an ideal situation, MSE is about equal to rock Unconfined Compressive Strength (UCS). When MSE>UCS, energy is wasted. Bit balling affects MSE. Also one can measure resulting penetration rate, torque and calculate MSE.

Referring to FIGS. 8-13, the replica bit 14 can be visually evaluated and/or weighed to determine the extent of bit balling. By visually inspecting the replica bit 14 through successive layers 34 in the test formation 16, one can identify which layers cause more balling and, likewise, one can compare bit designs to determine the effect the design has on balling. In addition, one can determine how different drilling fluids affect balling on the bit. For example, referring to FIGS. 10 and 13, one can see that there is substantially more balling on the replica bit in FIG. 10 than on the replica bit in FIG. 13.

Use of “pre-manufactured cuttings” instead of a solid rock sample allows use of printed, plastic, small-diameter replica bits. Test formations can consist of ground rock material blended with specific concentrations of reactive clay compressed to the proper consistency for testing. Bits can be coated with metallic materials to simulate the surface of actual bits. Testing can be conducted with different fluid designs. Equipment capable of calculating mechanical specific energy to aid in evaluation.

Applicants have found that balling achieved with the device is very similar to that encountered in the field. It is expected that effects of changing mud chemistry and bit design can be completed efficiently and cost-effectively by use of this equipment and procedure. Bit designs and fluids historically tested independently, or using expensive, time-consuming test equipment. See Paper SPE114673-MS, Bit Balling Mitigation in PDC Bit Design, by Michael Wells, PLUERE, Inc.; Tim Marvel and Chad Beuershausen, Hughes Christensen, IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, 25-27 Aug. 2008, Jakarta, Indonesia

Advantageously, the use of pre-manufactured cuttings provides consistently sized cuttings. By having the cuttings a consistent size, a formation can be precisely formulated. Further, formations can be repeatably formulated which allows a better comparison of bit designs. Additionally, bits “printed” on a 3-Dimensional printer from a 3-Dimensional CAD drawing can be used to easily check new bit designs.

While the claimed subject matter has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the claimed subject matter as disclosed herein. Accordingly, the scope of the claimed subject matter should be limited only by the attached claims. 

1. An apparatus for testing the effects of mud chemistry and bit design on bit balling comprising: a replica bit coupled to a rotary drive and having at least one nozzle; a test container; a test formation located within the container, wherein the test formation includes: a plurality of layers of pre-manufactured cuttings; a lifting device applying a force to the bottom of the test container to drive the test formation into the replica bit while the replica bit is rotated by the rotary drive; a second container within which is a drilling fluid; a conduit providing fluid communication from the second container to the replica bit; and a pump for circulating drilling fluid from the second container through the conduit to the replica bit.
 2. The apparatus of claim 1 further comprising a camera focused on the replica bit.
 3. The apparatus of claim 1, wherein the test container is transparent, and further comprising a camera located outside of the test container, wherein the camera is focused on the replica bit inside the test container.
 4. The apparatus of claim 1 further comprising a computer including inputs to track test parameters, wherein the test parameters include at least one of time, torque on the replica bit, rotary speed, and position of the replica bit relative to the bottom of the test formation.
 5. The apparatus of claim 4, wherein the computer is used to calculate at least one of weight on bit, rate of penetration, and mechanical specific energy.
 6. The apparatus of claim 1, wherein the pre-manufactured cuttings comprise ground rock material and reactive clay.
 7. The apparatus of claim 6, wherein the ground rock material is selected from the group consisting of shale, marble, a combination of shale and marble.
 8. The apparatus of claim 1, wherein the replica bit is a three-dimensionally printed, plastic model of a PDC bit.
 9. The apparatus of claim 8, wherein the replica bit is coated with a metallic finish.
 10. A method of testing the effects of mud chemistry and bit design on bit balling comprising: mixing a plurality of mixtures of ground rock material and reactive clay; layering the mixtures into a test container to create a test formation; coupling a replica bit to a rotary drive; fluidly connecting the replica bit to a second container containing drilling fluid; positioning the replica bit within the test container to a position above the test formation; rotating the replica bit; pumping fluid from the container and through the replica bit; and lifting the test formation to the rotating replica bit so that the bit rotates into the formation.
 11. The method of claim 10, further comprising: layering the mixtures into the test container such that the first layer loaded into the container has a lower concentration of reactive clay than the next successive layer and each successive layer has a higher concentration of reactive clay than the previous layer.
 12. The method of claim 10, further comprising: layering the mixtures into the test container such that the first layer loaded into the container has a higher concentration of reactive clay than the next successive layer and each successive layer has a lower concentration of reactive clay than the previous layer.
 13. The method of claim 10, wherein the mixtures are layered to create a formation with varied layers.
 14. The method of claim 10, wherein the mixtures are layered to create a formation with homogenous layers.
 15. The method of claim 10 further comprising measuring test parameters; wherein the test parameters include at least one of time, torque on the replica bit, rotary speed, and position of the replica bit relative to the bottom of the test formation.
 16. The method of claim 15 further comprising calculating at least one of rate of penetration, weight on bit, and mechanical specific energy.
 17. The method of claim 10 further comprising using a camera to video the replica bit as it is rotated through the formation.
 18. The method of claim 10 further comprising using a camera to take pictures of the replica bit as it is rotated through the formation. 